The Future of Needles: Upgrading Medicine's Most-Used Tool

Needles have existed in a form fairly similar to what we use today for thousands of years. But Jeffrey Karp has a new design—inspired by oil drilling—that, he hopes, will upgrade and automate the ubiquitous medical tool.

Electronic blood-pressure and insulin monitors, CAT scans, X-rays and MRIs have mechanized much of the medical process. But when it comes to inserting knives, needles and catheters into patients, clinicians around the world still do it the old fashioned way—by feel.

When inserting needles, doctors and nurses rely on tactile feedback, says Jeffrey Karp, chemical and bioengineering professor of the Harvard-MIT Division of Health Science and Technology. They use resistance of the tissue to know by feel where the needle is, so they know when the needle has reached its target. This clinical skill takes years to master, Karp says. Applying epidural anesthesia, for example, means pushing a needle through inches of tissue to reach a spot measuring only millimeters across and a doctor's miss can mean either dangerous complications—like a spinal fluid leak—or ineffective treatment. With this challenge in mind, Karp and a team of researchers devised a new model for the needle, featured in the Proceedings of the National Academy of Sciences on March 23. This needle can automatically find and enter the soft tissue the doctor is looking for and potentially avoid the dangers that come with doing it manually.

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Essentially, the new needle works like a simple clutch, a mechanism that locks to force two pieces to move together or releases to allow them to move separately. In a car, a clutch allows the wheels and engine to spin together while the car is moving—press the clutch when slowing down to decouple the two. Where a normal needle is straight, this needle has an S-shaped curve with a bendable piece of metal or plastic inside it. While the needle is strong enough to progress through tougher tissue like muscle, the filament bends back inside the needle. When it hits the target, the filament is fully pressed against the outside of the needle and locks in place, like an engaged clutch. At that point, the needle and its filament move together. But when the device finally reaches the soft spot—be it lung, stomach or blood vessel—the clutch disengages (see image below). The pressure is off the filament and it releases into the target area, and its rounded tip prevents it from breaking through the other side.

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Though most people associate a clutch with a car, the idea for an automatic needle actually came from the oil industry, according to Erik Bassett of Massachusetts General Hospital, who designed the prototype. A driller and a doctor have the same problem, Bassett says. They both must move blindly through a harder material—rock for the driller, tissue for the doctor—until they find their goal, a soft spot. A driller's nightmare is applying too much pressure, bending and ruining his equipment. Bassett turned that idea on its head. The research team intentionally designed the filament to bend back to create the friction needed for a clutch. The oil companies created mathematical models for bending under pressure so they could avoid this, Bassett says, but he used their numbers to design his prototype needle and its intentionally bending filament.

Anesthesiologist and team member Omar Farokhzad of Harvard Medical School began thinking about this project after finding that despite doctors' and nurses' intensive training, manual searching with needles still results in too many complications. Bassett says that if a needle near the spinal cord goes too far, for example, it can strike the dura mater that protects the spinal column, causing a days-long headache, or the spinal column itself, causing nerve damage. In the U.S. alone, the researchers say, doctors accidentally puncture the subarachnoid space of the central nervous system 75,000 times every year. That's why Bassett thinks it is critical that the new needle's clutch knows when to stop, releasing on its own and entering the low-pressure target area. "In that way, it's kind of an automatic system," he says.

Thus far, the team has tested its design on pigs. "They're relatively crude compared to what we'd need for a commercial application," Bassett says. Still, if a model for humans is approved, the clutch-based needle's simple design could be produced on a mass scale for pennies. And then, he says, clinicians could have something more than their own experience to guide them.